Method for decreasing lost circulation during well operation

Abstract

A method is provided for reducing lost circulation when aqueous, oil, or synthetic based drilling fluid is used. The method includes injecting two fluids into the well bore and lost circulation zone. The first fluid is an aqueous liquid containing at least one polymer capable of absorbing water in an alkaline environment. The aqueous liquid has a pH that inhibits at least one polymer from absorbing water. The second fluid contains a hardening composition in a base fluid having a pH sufficient to increase the pH in situ to allow at least one polymer to absorb water and expand with the absorbed water and substantially increase in size to close off the lost circulation zone and allow the hardening composition to create a plug in the well bore and set up.

1. A method for decreasing the loss of fluid in a wellbore to a subterranean thief zone in which well drilling or servicing operations are being conducted which comprises the acts of preparing a gellable composition comprising an acidic aqueous liquid and a superabsorbent polymer swellable at alkaline pH, introducing the gellable composition into the thief zone by way of the wellbore, and contacting the gellable composition with an alkaline hardenable composition slurry in an amount sufficient to provide the gellable composition with an alkaline pH. 
     
     
       2. The method of  claim 1  wherein the gellable composition has a pH less than about 4.5. 
     
     
       3. The method of  claim 1  wherein the alkaline pH is at least about 8. 
     
     
       4. The method of  claim 1  wherein the gellable composition further comprises chitosan. 
     
     
       5. The method of  claim 4  wherein the chitosan has a degree of acetylation of 0% to about 40%. 
     
     
       6. The method of  claim 4  wherein the acidic aqueous liquid contains sulfamic acid therein. 
     
     
       7. The method of  claim 6  wherein the gellable composition contains the superabsorbent polymer, chitosan, and sulfamic acid in a weight ratio of 20% to 50% superabsorbent polymer, 30% to 55% chitosan, and 10% to 40% sulfamic acid, and wherein the total concentration of superabsorbent polymer, chitosan, and sulfamic acid is from about 5 pounds per 42 gallon barrel to about 25 pounds per 42 gallon barrel. 
     
     
       8. The method of  claim 1  wherein the hardenable composition slurry comprises diatomaceous earth, a suspending agent, lime, a loss control material, sodium silicate, and sulfate. 
     
     
       9. The method of  claim 8  wherein the suspending agent is finely divided paper. 
     
     
       10. The method of  claim 8  wherein the loss control material comprises micronized cellulose fiber. 
     
     
       11. The method of  claim 1  wherein the contacting comprises squeeze injection of the alkaline hardenable composition slurry into the thief zone.